I have an Exchange 2010 Hosted environment and now I installed new Sharepoint 2010 Farm. My issue is that Outlook Web Parts won't work with Single Sign On and I have to log in twice. First time to Sharepoint site and second time to OWA. Is there any way to make it working with SSO. All my servers (Exchange and Sharepoint) are connected to the same domain.

1 Answer
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The exchange webparts are just using an iframe to display a subset of outlook web application (OWA) functions. Do you have OWA set up? If the user is requested to enter credentials to the OWA url you will get the same for the webpart in SharePoint.

In the first place the user if integrated into the domain (domain joined desktop/laptop) using IE should not get a credential prompt. If it is prompted you have to configure the SharePoint URL into the trusted sites so the logon credentials are send by default. SharePoint "must" be setup using NTLM or even better Kerberos. Otherwise clients from vista or higher are not sending any credentials to basic auth websites. Do the same stuff for owa and you won't see credentials.

What do you mean by "having OWA set up"? OWA is working properly for all users. My problem is that it is not passing through credentials from Sharepoint site to OWA webpart while it is the same user and I'm already logged in to Sharepoint.
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PrzemekDec 18 '12 at 20:54

That's what i told you. The OWA webpart is just an iframe. Check the owa web part configuration and the url's used. SharePoint is not passing any credentials to owa. The Client is passing the credentials to owa and SharePoint is just providing the HTML to embed the owa URL. Microsoft took this approach because otherview anybody would have to implement Kerberos with Delegation to get this stuff working. This is no easy part so Microsoft stuck to using just the owa parts using an iframe. You can use IE developer Tools or fiddler to see what the Client is doing on what Server.
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Marco ScheelDec 19 '12 at 11:59